The following is a list of the IRMA's number-one singles of 1998. The dates shown below are Sundays.
| Issue Date | Song | Artist |
|---|---|---|
| 4 January | "Perfect Day" | Various Artists |
| 11 January | ||
| 18 January | "All Around the World" | Oasis |
| 25 January | ||
| 1 February | "Doctor Jones" | Aqua |
| 8 February | ||
| 15 February | "My Heart Will Go On" | Celine Dion |
| 22 February | ||
| 1 March | ||
| 8 March | ||
| 15 March | ||
| 22 March | ||
| 29 March | "It's Like That" | Run-D.M.C. vs. Jason Nevins |
| 5 April | ||
| 12 April | ||
| 19 April | ||
| 26 April | "All That I Need" | Boyzone |
| 3 May | ||
| 10 May | ||
| 17 May | "Feel It" | The Tamperer featuring Maya |
| 24 May | ||
| 31 May | ||
| 7 June | "C'est La Vie" | B*Witched |
| 14 June | ||
| 21 June | ||
| 28 June | ||
| 5 July | ||
| 12 July | ||
| 19 July | "Ghetto Supastar" | Pras Michel feat. Mýa and Ol' Dirty Bastard |
| 26 July | ||
| 2 August | ||
| 9 August | "No Matter What" | Boyzone |
| 16 August | ||
| 23 August | ||
| 30 August | ||
| 6 September | ||
| 13 September | ||
| 20 September | "Millennium" | Robbie Williams |
| 27 September | ||
| 4 October | ||
| 11 October | "I Don't Want to Miss a Thing" | Aerosmith |
| 18 October | ||
| 25 October | "Sweetest Thing" | U2 |
| 1 November | ||
| 8 November | "Irreplaceable" | Kerri Ann |
| 15 November | "Believe" | Cher |
| 22 November | ||
| 29 November | ||
| 6 December | ||
| 13 December | ||
| 20 December | ||
| 27 December | "Goodbye" | Spice Girls |